The recent development of well-defined ruthenium and molybdenum metathesis catalysts has generated renewed interest in methods for selective cross-metathesis of terminal olefins. For example, Crowe et al. have demonstrated that c-substituted terminal olefins such as styrene and acrylonitrile can be used to efficiently nationalized terminal olefins. Crowe has also reported a useful terminal olefin cross-coupling procedure utilizing nucleophillic species such as allyl trimethylsilane. More recently, Blechert et al. have shown that certain sterically hindered terminal olefins do not undergo self-metathesis and can be functionalized with a number of commercially available terminal olefins using ruthenium and molybdenum catalysts. The homologation of homoallylglycine derivatives has been reported by Gibson et al. Finally, both cross yne-ene and ring-opening cross metathesis reactions using Ru and Mo catalysts have been demonstrated. Unfortunately, these reactions tend to be slow, non-selective with relatively low product yields. As a result, large scale reactions for commercial applications are generally unfeasible using prior known methods.
The present invention relates to a method for making disubstituted internal olefin products from a first terminal olefin and a second terminal olefin. In general, the first terminal olefin is reacted with itself to form a dimer intermediate. The dimer is then reacted with the second olefin to yield the disubstituted internal olefin product. A schematic illustration of this concept is as follows:
XCHxe2x95x90CH2+XCHxe2x95x90CH2xe2x86x92XCHxe2x95x90CHX+YCHxe2x95x90CH2xe2x86x92XCHxe2x95x90CHY.
Dimerization of one of the initial terminal olefins unexpectedly results in faster rates of reaction, enhanced trans selectivity, and improved product yield.
A typical reaction scheme for cross metathesis of two terminal olefins is as follows:
XCHxe2x95x90CH2+YCHxe2x95x90CH2xe2x86x92XCHxe2x95x90CHY
wherein X and Y are independently an alkyl or aryl optionally substituted with one or more alkyl or aryl substitutent groups. X and Y may also optionally include one or more functional groups. Illustrative examples of suitable functional groups include but are not limited to: hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen.
It has been unexpectedly discovered that dimerizing one of the initial terminal olefins results in faster rates of reaction, enhanced trans selectivity, and improved product yield. Dimerization to form a disubstituted olefin intermediate was inspired by the synthesis of telechelic polymers via ring opening polymerization/cross metathesis reaction as shown below. 
The present invention is a variation of this theme to make a disubstituted internal olefin product from a first terminal olefin and a second terminal olefin. As an initial matter, the first terminal olefin is reacted with itself to form a dimer. The dimer is then reacted with the second olefin to yield the disubstituted internal olefin product. A schematic illustration of this concept is as follows:
XCHxe2x95x90CH2+XCHxe2x95x90CH2xe2x86x92XCHxe2x95x90CHX+YCHxe2x95x90CH2xe2x86x92XCHxe2x95x90CHY.
Any suitable metathesis catalyst may be used. Illustrative examples of suitable catalysts include ruthenium and osmium carbene catalysts as disclosed by U.S. Pat. Nos.: 5,342,909; 5,312,940; 5,728,917; 5,750,815; 5,710,298, 5,831,108, and 5,728,785, all of which are incorporated herein by reference. Briefly, the ruthenium and osmium carbene catalysts possess metal centers that are formally in the +2 oxidation state, have an electron count of 16, are penta-coordinated, and are of the general formula 
wherein:
M is ruthenium or osmium;
X and X1 are each independently any anionic ligand;
L and L1 are each independently any neutral electron donor ligand;
R and R1 are each independently hydrogen or a substitutent selected from the group consisting of C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl. Optionally, each of the R or R1 substitutent group may be substituted with one or more moieties selected from the group consisting of C1-C10 alkyl, C1-C10 alkoxy, and aryl which in turn may each be further substituted with one or more groups selected from a halogen, a C1-C5 alkyl, C1-C5 alkoxy, and phenyl. Moreover, any of the catalyst ligands may further include one or more functional groups. Examples of suitable fictional groups include but are not limited to: hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen.
In preferred embodiments of these catalysts, the R substitutent is hydrogen and the R1 substitutent is selected from the group consisting C1-C20 alkyl, C2-C20 alkenyl, and aryl. In even more preferred embodiments, the R1 substitutent is phenyl or vinyl, optionally substituted with one or more moieties selected from the group consisting of C1-C5 alkyl, C1-C5 alkoxy, phenyl, and a functional group. In especially preferred embodiments, R1 is phenyl or vinyl substituted with one or more moieties selected from the group consisting of chloride, bromide, iodide, fluoride, xe2x80x94NO2, xe2x80x94NMe2, methyl, methoxy and phenyl. In the most preferred embodiments, the R1 substitutent is phenyl.
In preferred embodiments of these catalysts, L and L1 are each independently selected from the group consisting of phosphine, sulfonated phosphine, phosphite, phosphinite, phosphonite, arsine, stibine, ether, amine, amide, imine, sulfoxide, carboxyl, nitrosyl, pyridine, and thioether. In more preferred embodiments, L and L1 are each a phosphine of the formula PR3R4R5, where R3, R4, and R5 are each independently aryl or C1-C10 alkyl, particularly primary alkyl, secondary alkyl or cycloalkyl. In the most preferred embodiments, L and L1 ligands are each selected from the group consisting of xe2x80x94P(cyclohexyl)3, xe2x80x94P(cyclopentyl)3, xe2x80x94P(isopropyl)3, and xe2x80x94P(phenyl)3.
In preferred embodiments of these catalysts, X and X1 are each independently hydrogen, halide, or one of the following groups: C1-C20 alkyl, aryl, C1-C20 alkoxide, aryloxide, C3-C20 alkyldiketonate, aryldiketonate, C1-C20 carboxylate, arylsulfonate, C1-C20 alkylsulfonate, C1-C20 alkylthio, C1-C20 alkylsulfonyl, or C1-C20 alkylsulfinyl. Optionally, X and X1 may be substituted with one or more moieties selected from the group consisting of C1-C10 alkyl, C1-C10 alkoxy, and aryl which in turn may each be further substituted with one or more groups selected from halogen, C1-C5 alkyl, C1-C5 alkoxy, and phenyl. In more preferred embodiments, X and X1 are halide, benzoate, C1-C5 carboxylate, C1-C5alkyl, phenoxy, C1-C5alkoxy, C1-C5alkylthio, aryl, and C1-C5 alkyl sulfonate. In even more preferred embodiments, X and X1 are each halide, CF3CO2, CH3CO2, CFH2CO2, (CH3)3CO, (CF3)2(CH3)CO, (CF3)(CH3)2CO, PhO, MeO, EtO, tosylate, mesylate, or trifluoromethanesulfonate. In the most preferred embodiments, X and X1 are each chloride.
For the purposes of clarity, the specific details of the present invention will be illustrated with reference to especially preferred embodiments. However, it should be appreciated that these embodiments and examples are for the purposes of illustration only and are not intended to limit the scope of the present invention.
A particularly useful application for the inventive method is in the homologation of terminal alkenes. The terminal alkene may be hindered or unhindered. As shown by Table 1, treatment of a terminal olefin such as 9-decen-1-yl benzoate (2a) with 1-2 equivalents of a symmetric internal olefin and 5 mol % ruthenium benzylidene 1 in refluxing dichloromethane provided the desired cross metathesis products in good yields. The reactions proceed largely to completion and the starting material homodimer can be easily recovered and recycled in a subsequent cross-metathesis step. In general, the inventive method favors the formation of the trans olefin isomer. For example, high trans selectivity was observed with cis-1,4-butenediol derivatives bearing bulky protecting groups.
Table 1 shows examples of cross metathesis reactions:
Table 1 charts the cross-metathesis product yields of example substrates. The percentage product yields (product(%)) reflects isolated product yields. The E/Z ratio was determined by 1H-NMR integration. Initial efforts focused upon the elaboration of terminal olefins to the corresponding allylic alcohol derivatives. The commercially available cis-2-butene-1,4-diol diacetate (entry 1) provided the homologated allylic acetate in excellent yield (89%, 4.7:1 E/Z) using two equivalents of internal olefin in refluxing dichloromethane. When only one equivalent of diacetate was used, the yield decreased (77%) and no significant change in the transcis ratio was observed (entry 2). The use of two equivalents of diacetate was found to be more efficient than simply using one, two, or four equivalents of allyl acetate (entries 3-5). Employing the diol acetate as solvent (55 equiv., 45xc2x0 C., 12 h) increased the isolated yield to 91%, although with diminished trans olefin content (3:1 E/Z).
Good cross metathesis yields and improved trans selectivity were also found for several ether derivatives of cis-1,4-butenediol (entries 6-8). In entry 6, the 77% product yield was determined after TBAF deprotection of TBS ether. In entry 8, the 71% product yield was determined after H2/Pdxe2x80x94C hydrogenation-hydrogenolysis of allyl benzyl ether. The compatibility of nitrogen-containing substrates was probed through the cross-metathesis of Boc-protected cis-1,4-diaminobutene (entry 9), which provides a direct route to protected allylic amines. Trans disubstituted internal olefins were also found to be reactive. Namely, dimethyl trans-3-hexene-1,6-dioate (entry 10 ) provided the desired homoallylic ester cross product as the major product (74%, 3:1 E/Z; recovered homodimer 3a: 23%). These results demonstrate that both cis or trans disubstituted internal olefms could be used as efficient coupling partners in cross metathesis reactions.
Several examples of the inventive method are as follows: 
Dimerization of neat substances (2a-c) with 0.3 mol % 1 in vacuo provided mostly trans (4:1) disubstituted olefins in high yield. Homodimer 3b was subsequently used to functionalized 2,3,4,6-tetra-O-benzyl-1-xcex1-C-allylglucoside (4) in 73% yield (3:1 e/Z. recovered homodimer of 4: 19%). By comparison, the synthesis of 5 using four equivalents of terminal olefin 2b resulted in a marginally lower yield with slightly lower trans selectivity (68%, 2.2:1 E/Z). Olefin 3b was also used to successfully transform N-Boc-Serine-(O-Allyl)-OMe into lipophilic amino acid 7 in excellent yield and improved trans selectivity (85%, 6:1 E/Z). Cross coupling reactions using 9-decenyl-1-yl N-Boc glycinate (2c) and various equivalents of 9-decen-1-yl acetate (2b) or the internal olefin homodimer 3b demonstrate an advantage to adjusting the stoichiometry of a terminal olefin component in cross-metathesis reactions involving two isolated terminal olefins.
In sum, practice of the present invention results in the synthesis of disubstituted internal olefins in good yield and with improved trans selectivity. A particularly promising application of the inventive method is in the homologation of terminal olefins. The inventive method is also useful for the functionalization of advanced intermediates in multistep synthesis and for the construction of heterodimeric molecules for research in molecular biology.